I'm coming into this a little late, but I'll throw in some points.
Channel Divinity: I think the way you had it going the first time was better. You only have one use of channel divinity per rest, so it isn't going to happen a ton. I don't think it was overpowered before.
Concentration Breaker: After you hit a creature with an attack, you may use your channel divinity to end one magical effect on that creature or break the concentration of any spells they are concentrating on.
Magical Resilient: You may use your channel divinity to automatically succeed on a saving throw. Additionally, you are immune to any effects that occur on a successful save.
Aura of Anti-Magic: Its hard to define arcane magic in this edition. Why not just advantage on saving throws vs spells and/or magical effects in general? I think the benefits of not having to answer what is arcane and what isn't are worth it.
You already have Counterspell given as a class spell. How about instead at 15 you gain resistance to damage from magical spells and effects?
Magic Immunity: This might be a little much, as it gives a ton of absolute benefits. I also don't really think that magical weapons really fit into the goal you are trying to go after, which is fighting magic users. If we model it off of some of the other subclass 20th level abilities as an aura, what about:
You become enamored with holy protection versus magic. Your body shimmers with holy darkness, dimming sources of magical light near you.
Any creature that wishes to target you with a harmful spell or magical effect must make a successful wisdom saving throw against your spell DC or the spell fails.
You emanate an aura of arcane denial around you in a 30 foot radius. Anytime an enemy creature attempts to cast a spell inside this aura, it must succeed on a wisdom saving throw or the spell fails.